Pancreatic cancer is a leading cause of cancer-related mortality in the United States with an estimated 32,000 deaths annually. Activating mutations in the KRAS2 oncogene, amplification of the AKT2 oncogene, and loss of the TP53, INK4A, and MADH4 tumor suppressor genes, commonly occur in this disease. However, the precise signaling perturbations that occur as a consequence of these genetic changes are still poorly understood. For example, although activating mutations in the KRAS2 oncogene occur in approximately 90% of pancreatic ductal adenocarcinomas, the relative contributions of the various Ras-stimulated signaling pathways - mediated by Raf, PI3-kinase, and RalGEFs - to the pathogenesis of the disease are unknown. Therefore, this application describes the use of a novel mouse model for pancreatic ductal adenocarcinoma (PDAC), generated through the somatic introduction of oncogene-encoding avian retroviruses into the pancreata of transgenic mice expressing the avian retroviral receptor, TVA, specifically within the pancreatic duct epithelium, to identify the relative contributions of K-Ras-stimulated signaling pathways to tumor initiation, maintenance, and progression. This proposal seeks to answer the following questions: 1) What are the consequences of somatic and sporadic activation of Ras signaling in the pancreatic duct epithelium? 2) What are the roles of the various Ras-activated signaling pathways in PDAC? And 3) What are the gene expression signatures associated with the activation of Ras-regulated signaling pathways in pancreatic tumors? To identify the immediate consequences of Kras gene activation in pancreatic duct epithelial cells (PDECs) and the roles played by individual downstream effector pathways, viruses encoding an activated Kras allele, or Kras alleles that preferentially lead to the activation of individual downstream pathways, will be introduced into PDECs and the effect on cell proliferation and apoptosis determined. In addition, tumors will be induced in vivo by the introduction of viruses encoding K-Ras or K-Ras effector mutants into the pancreata of TVA transgenic mice, and the tumor phenotypes analyzed by histology, immunostaining and biochemical methods. Furthermore, through the use of small molecule inhibitors and RNA interference methods, the requirement for specific Ras-stimulated signaling pathways for sustained tumor cell proliferation and survival will be established. Finally, gene expression profiling will be performed to identify: (i) Gene expression changes associated with the early steps of K-Ras-mediated transformation of pancreatic duct epithelial cells;(ii) A gene expression signature associated with K-Ras-induced pancreatic ductal tumors;and (iii) Gene expression signatures associated with the activation of specific Ras-stimulated downstream pathways. Such gene expression signatures may potentially be used as diagnostic tools, as well as surrogate markers for response to targeted therapeutic interventions.